1. Field of the Invention
This invention relates to infrared detectors and, more particularly, to such a detector combined with a dewar in an assembly which is adapted as a common module for plug-to-plug compatibility with related common module elements making up a detection system.
2. Description of the Background Art
Dewar detector assemblies of the type to which the present invention is directed have been known for a number of years. Presently known designs center around modular metal and glass construction and include a vacuum-metallized glass dewar bore (commonly referred to as a coldfinger); a glass-to-metal sealed feedthrough assembly having radially directed leads; an indium sealed dewar window; a replaceable evacuation tube; and a getter system that can be reactivated.
The glass coldfinger may be considered the heart of an inner assembly. It is a cylindrical hollow glass member, closed at one end, which supports the infrared detector assembly and provides cooling and thermal isolation for the detector. The detector comprises an array of individual infrared detector elements. The optical input to the array is usually directed by one or more scanning mirrors.
A vacuum-metallized laser-delineated gold conductor pattern on the glass coldfinger carries signal and common leads from the detector array at the end or "platform" of the coldfinger. This gold conductor pattern extends across the end, then over the edge and down the exterior walls of the coldfinger. It will be appreciated that this is an extremely fragile element, very difficult and expensive to fabricate, particularly with the uniformity which is required for replaceable elements. Moreover, the structure of the feedthrough assembly and the arrangement for making connections to the gold conductor pattern on the outer wall of the coldfinger present substantial difficulties in making reliable connections. Circuit connections are provided via a pattern of 220 ribbon-type leads which are thermocompression-bond to the coldfinger conductors. Annular glass-epoxy feedthrough boards containing contact pins are individually soldered to each eyelet in the lead pattern. These in turn are individually soldered to four flexible flat ribbon cables which carry the signals to four quadrant sectors of the common module plug connector. Again, the connections between the ends of the ribbon cable conductors and the pins of the common module plug connector are individually soldered.
The considerable number of solder connections in the signal paths of the common module circuitry and the structural design of the coldfinger, in which the signal paths from the detector are formed of very fine gold lines extending along the circumferential surface of the cylindrical coldfinger, have resulted in certain problems with respect to production capability, fabrication cost, reliability and maintenance. Improvements in design and the use of other fabrication techniques could lead to solutions to certain of these problems.
For example, techniques are known for making electrical connections without the need for soldering. One such technique is disclosed in U.S. Pat. No. 4,125,310. That patent discloses the fabrication of printed circuit contact terminations having a plurality of copper buttons covered with a very thin layer of gold plating. A plurality of these contacts, mounted on a wafer in opposed juxtaposition to a corresponding pattern of adjacent circuit contacts, is brought together with the other circuit terminations and pressure is applied sufficient to force flow of the gold layer to develop a tight physical seal between the opposed surfaces which in turn, produces a reliable electrical connection. Such an arrangement lends itself to separation and resealing of the contact arrays, thereby being appropriate for use in the new common module of the present invention which is amenable to disassembly for repair and/or replacement of defective component parts.
Because of various problems as noted above with respect to cost, production capabilities, and maintenance, a new common module design is desired which would present substantial improvement over the aforementioned art and which would eliminate or minimize the problems which have been noted.